So then your answer is simple- just like in Flask, put the function wherever it makes sense for your application and desired architecture.
If you really prefer SQLAlchemy, there is nothing stopping you from using it over the Django ORM, I happen to prefer the Django ORM, but Django doesn't get jealous if you go out with a different ORM (it is a polyamorious web framework[1]).
Yes, I have seen Django applications do that. There are plenty of individuals out there advocating such a separation. I wouldn't worry about these "different developers' and their opinions.
[1] I was going to use a smiley face here, but then I recalled that a Python dev was de-flocked recently for using smiley emoji as it is offensive to some individuals, so insert whatever words or symbols you don't find offensive that indicate humor instead.